FIG. 1 illustrates an exemplary wafer probing system 100 for testing the dies on a semiconductor wafer. In the exemplary system 100 shown in FIG. 1, a newly manufactured semiconductor wafer 124 comprising dies (not shown) to be tested is secured on a working surface 128 of a chuck 126 that is part of a moveable stage 112 inside a prober 109. The stage 112 moves the wafer 124 into contact with probes 122 of a probe card assembly 110. More specifically, bond pads (not shown) on the dies (not shown) of the wafer 124 are brought into contact with the probes 122, which establishes electrical connections between the dies (not shown) of the wafer 124 and the probes 122.
The tester 102 then generates test data patterns that are written into the dies (not shown), and the tester 102 evaluates response data generated by the dies to determine whether individual dies pass or fail the testing. The test data travels from the tester 102 through a communication link 104 to a test head 106. (Communications link 105 may also be provided for controlling the prober 109 as shown in FIG. 1.) From the test head 106, the test data travels through electrical connectors 108 (e.g., pogo pins) to the probe card assembly 110, which provides electrical connections to the probes 122. Response data generated by the dies (not shown) of wafer 124 travel in the reverse direction to the tester 102.
The probe card assembly 110 may be made and configured in any number of ways. The exemplary probe card assembly 110 shown in FIG. 1 includes a probe board 118 and a probe substrate 120, which are secured one to the other. The probe board 118 is attached by securing mechanism 116 (e.g., clamps or bolts) to a prober head plate 114. FIG. 2 illustrates a top view of a simplified prober head plate 114 that includes holes 202 for securing mechanism 116 and an opening 204 that allows electrical connectors 108 to contact probe board 118. Once the probe card assembly 110 is secured inside the prober 109, the stage 112 may move the wafer 124 into contact with the probes 122 as discussed above. U.S. Pat. No. 5,974,662 (which is incorporated herein by reference) discloses another exemplary probe card assembly.
It is often important that the prober head plate 114 and the working surface 128 of chuck 126 be planar with respect to each other within a specified tolerance. The specified tolerance typically depends on the particular probing application. If the prober head plate 114 and the working surface 128 of the chuck 126 are too far out of planarity, it may be difficult or impossible to properly connect electrically the dies (not shown) of wafer 124 with probes 122.
Typically, the test head 106 and the probe card assembly 110 must be removed from the prober 109 to planarize the prober head plate 114 with respect to the chuck surface 128. For example, probe card assembly 110 is unbolted and removed from the prober head plate 114, and the test head 106 is detached and removed from the prober 109. In some probers, the test head 106 may alternatively be loosened so that it is moveable yet still attached to the prober 109 and then tilted or otherwise moved out of its “test position” (i.e., the position of test head 106 during normal operation to test a semiconductor device or other electronic device disposed on the chuck 126), allowing access to the prober head plate 114 and chuck 126. With the probe card assembly 110 and test head 106 removed (or at least moved out of the way), workers manually measure distances between the prober head plate 114 and the surface 128 of the chuck 126 and adjust the planarity of the prober head plate 114 until the measurements indicate that the prober head plate 114 is planar with the chuck 126 (within an acceptable tolerance). Thereafter, the test head 106 is moved back into position and resecured to the prober 109, and the probe card assembly 110 is reattached to the prober head plate 114.
Not only is it time consuming and labor intensive to move and then replace the test head 106 and the probe card assembly 110, but the weight of the test head 106 (which often weighs about 200 pounds) may cause the prober 109 and/or the prober head plate 114 to shift or flex and thereby cause the prober head plate 114 to be out of planarity with the chuck 126 after the test head 106 is resecured to prober 106 in a test position. There is, therefore, a need for an improved method and apparatus for measuring the planarity of a prober head plate 114 with respect to a surface 128 of a chuck 126.
It should be noted that the wafer probing system 100 of FIG. 1 is but one example of a system in which a device is brought into contact with a plurality of probes in order to test, monitor, or operate the device. Other examples include systems for burning in semiconductor dies, systems for testing singulated dies (packaged or unpackaged), and systems for testing other electronic components, such as electronics modules. In many such systems, it is important that the planarity of an apparatus (e.g., the prober head plate 114) that holds a probing device (e.g., the probe card assembly 110) be within a specified tolerance of an apparatus (e.g., the chuck 126) that holds the device to be probed (e.g., the wafer 124). Therefore, the above described need for an improved method and apparatus for measuring planarity is generally applicable to any application in which the planarity of a first structure with respect to a second structure is measured, determined, and/or adjusted.